In general, a vehicle is provided with a heat exchange-type cooling system, such as a radiator or oil cooler, in addition to an air conditioning system for cooling an interior of a vehicle. A radiator is a heat exchanger configured such that coolant is circulated inside the engine to absorb heat generated by combustion of an engine, and then the high temperature coolant passes through the radiator by using a water pump, and emits the heat outside the engine. Thus, the radiator prevents an engine from overheating, and maintains an optimal driving condition.
Furthermore, though an engine or transmission for a vehicle is filled with oil so as to be lubricated or sealed, when oil is overheated, viscosity of oil is decreased and the above purposes of lubrication and sealing may not be achieved. Particularly, an engine or other components for a vehicle may be damaged when the engine or the other components are not properly lubricated. In this case, an oil cooler for cooling oil is utilized to prevent this problem.
Since an engine is considerably heated while driving, temperatures of coolant and oil are also increased, and thus a radiator and oil cooler cool coolant and oil, respectively. Meanwhile, when a temperature of oil is decreased, viscosity of oil is increased. Thus, in a cold environment, an engine for a vehicle is started in a state where viscosity of oil is high. In this case, if oil is further cooled by using an oil cooler, an engine or other components for a vehicle may be damaged. This damage is called cold shock. Accordingly, various ways to prevent cold shock are used, for example, an oil cooler is not operated when an engine is started, or a warmer for heating oil is operated.
FIG. 1 is a view illustrating a transmission oil heat exchange system according to the related art.
In general, coolant circulated around an engine 10 is circulated along a full line shown in FIG. 1 by passing through a coolant heater 30, a first heat exchanger 40 (generally referred to simply as a warmer), a radiator 60, and a second heat exchanger 50 (generally referred to simply as a cooler). Furthermore, transmission oil filling a transmission 20 is circulated along a dotted line shown in FIG. 1. That is, the transmission oil passes through the first and second heat exchangers 40 and 50, and returns to the transmission 20.
When an outside temperature is low as in a winter season, a temperature of transmission oil is also decreased, thereby increasing viscosity of the transmission oil. Thus, when an engine is started, cold shock may occur in the transmission 20 due to increased viscosity of transmission oil. Accordingly, at a cold start of an engine, transmission oil passes the first heat exchanger 40 for heat exchange between the transmission oil and coolant heated by the heater 30, and the transmission oil is partially heated. Further, the transmission oil passes through a bypass valve 70 and a returning valve 80 that are formed in a three way valve shape, and returns to the transmission 20.
Meanwhile, since transmission oil is considerably heated while normally driving, the transmission oil should be partially cooled. In this case, the coolant heater 30 that is operated at a cold start of an engine is turned off after an engine is driven for a predetermined period. Thus, a temperature of coolant introduced into the first heat exchanger 40 is lower than a temperature of transmission oil, and the transmission oil introduced into the first heat exchanger 40 is partially cooled by exchanging heat between the transmission oil and the coolant. However, when a temperature of the transmission oil is considerably high, since the transmission oil cannot be sufficiently cooled at the first heat exchanger 40, the transmission oil having passed through the first heat exchanger 40 is introduced into the second heat exchanger 50 through the bypass valve 70, is cooled once again, and returns to the transmission 20 through the returning valve 80.
As described, in order to change a flow direction of transmission oil depending on a temperature of the transmission oil, a thermostat (not shown) for measuring a temperature of the transmission oil and a control device (not shown) for controlling the bypass valve 70 should be separately provided. Thus, it is problematic in that the structure of the system is complicated. Furthermore, it is also problematic in that since the bypass valve 70 for controlling a flow direction of transmission oil is separately provided from the first heat exchanger 40, assembly process of the system is complicated, thereby decreasing productivity.